A comparison of effects of zearalenone and estradiol benzoate on reproductive function during the estrous cycle in gilts

Effects of estradiol benzoate (EB) and zearalenone (Z) on luteal maintenance and plasma hormone concentrations were studied in 45 gilts. Gilts were allocated to receive either 20 mg Z, 2 mg EB or no treatment (C) on d 1 to 5 (T1), 6 to 10 (T2) or 11 to 15 (T3) of an estrous cycle (five per treatment). Onset of estrus was designated as d 0 of the estrous cycle. Zearalenone was added to the daily ration and EB was administered via an intramuscular injection. Blood samples were collected every 10 min over a 4-h period on the first 2 d prior to onset of treatment; the first, third and fifth days of treatment; and the first two and the fifth day after the end of the treatment periods. Gilts receiving EB and Z during T2 and T3 had longer (P less than .05) inter-estrous intervals than C gilts. The range in inter-estrous intervals for Z and EB treatments was 28 to 74 and 27 to 63 d, respectively. Mean plasma progesterone concentrations were elevated (P less than .05) during T2 and T3 in EB and Z-treated gilts when compared with C females. Estradiol benzoate treatment during T2 and T3 reduced (P less than .05) mean plasma luteinizing hormone (LH) concentrations more than C or Z treatments. Mean plasma concentrations of 13, 14-dihydro-, 15-keto-prostaglandin F2 alpha (PGFM) during T3 were higher (P less than .05) in C and Z gilts on d 13 and 15 post-estrus when compared with EB gilts.(ABSTRACT TRUNCATED AT 250 WORDS)     

Enhancement of ovulation rate in gilts by increasing dietary energy and administering insulin during follicular growth

Two experiments were conducted to examine influences of dietary energy and insulin on ovulation rate and patterns of luteinizing hormone (LH), follicle stimulating hormone (FSH), glucose, insulin and estradiol in gilts during 6 d before estrus. In Exp. 1, 36 gilts were given altrenogest for 14 d to synchronize estrus. In a factorial arrangement, gilts were fed one of two levels of dietary energy (5,771 or 9,960 kcal metabolizable energy (ME)/d), and given one of two levels of porcine insulin (0 or .1 IU/kg body weight iv every 6 h). Dietary treatments began 4 d before and insulin treatments began 1 d after the last day of altrenogest, respectively, and lasted until 24 h after estrus. Main effect means for number of corpora lutea were 14.0 +/- 1.3 and 17.6 +/- .9 for 5,771 and 9,960 kcal ME (P less than .05), and 14.6 +/- 1.0 and 17.0 +/- .9 for 0 and .1 IU insulin (P less than .05). Number of LH peaks on d 3 was greater for gilts that received 9,960 kcal than 5,771 kcal (3.3 +/- .2 vs 2.7 +/- .2; P less than .05), and for .1 than 0 IU insulin (3.2 +/- .2 vs 2.7 +/- .2; P less than .05). During the first 24 h of sampling, concentrations of LH and FSH were greater (P less than .05) in gilts receiving 9,960 kcal ME plus insulin than for other treatment combinations. Concentrations of estradiol were not affected by treatments. In Exp. 2, two formulations of insulin were evaluated for influence on ovulation rate. All gilts received altrenogest and 9,960 kcal ME/d as in Exp. 1. Then on the first day after altrenogest, seven gilts each received short-acting insulin (as in Exp. 1), long-acting insulin (zinc suspension, 1.0 IU/kg body weight every 18 to 24 h), or served as controls. Ovulation rates were increased (P less than .05) by both insulin preparations (15.6, control; 19.1, short-acting; 18.5, long-acting; SE = 1.2). Concentrations of LH tended to be greater after short-acting insulin, but differences were not significant (P = .13). We conclude that increases in ovulation rate produced by dietary energy and insulin are not necessarily accompanied by changes in gonadotropins or estradiol.     

Characterization of gonadotropic and ovarian steroid hormones during the periovulatory period in high ovulating select and control line gilts

Cyclic gilts from Control (C, randomly selected, n = 11) and Relax Select (RS, nine generations of selection for increased ovulation rate followed by seven generations of relaxed or random selection, n = 9) lines of the University of Nebraska Gene Pool population (derived from 14 different breeds) were utilized to characterize differences in gonadotropic and ovarian steroid hormones during preovulatory and postovulatory phases of the estrous cycle. Blood samples were collected during four periods (0500, 1100, 1700 and 2300) daily beginning 2 d prior to anticipated estrus (d -2, d 18 of a 20-d estrous cycle), and continuing through d 4 postestrus (d 0 = 1st of standing estrus). Sampling within a period consisted of five blood samples at 15-min intervals. All plasma samples were analyzed for concentrations of follicle stimulating hormone (FSH) and luteinizing hormone (LH). Neither mean LH nor peak concentration of LH during the preovulatory surge differed between genetic lines (P greater than .10). Concentrations of FSH increased faster (line X period, P less than .05) and tended (P less than .1) to peak at a higher concentration in RS (.88 ng/ml) than in C (.54 ng/ml) gilts (P less than .05) during the 12 h preceding the FSH and LH preovulatory peaks. The second FSH surge began approximately 24 h after the preovulatory FSH peak. Peak FSH concentrations were observed at 42 h in both lines (1.46 vs 1.74 ng/ml for C and RS gilts, respectively). The higher FSH concentration in RS gilts established during the preovulatory surge was maintained through the second FSH surge (P less than .01). No line differences were detected in plasma concentrations of estradiol-17 beta and progesterone.     

Plasma gonadotropins and ovarian hormones during the estrous cycle in high compared to low ovulation rate gilts

Mature gilts classified by low (12 to 16 corpora lutea [CL], n = 6) or high (17 to 26 CL, n = 5) ovulation rate (OR) were compared for plasma follicle-stimulating hormone (FSH), luteinizing hormone (LH), progesterone, estradiol-17beta, and inhibin during an estrous cycle. Gilts were checked for estrus at 8-h intervals beginning on d 18. Blood samples were collected at 8-h intervals beginning on d 18 of the third estrous cycle and continued for one complete estrous cycle. Analysis for FSH and LH was performed on samples collected at 8-h intervals and for ovarian hormones on samples collected at 24-h intervals. The data were standardized to the peak of LH at fourth (d 0) and fifth estrus for the follicular phase and analyzed in discrete periods during the periovulatory (-1, 0, +1 d relative to LH peak), early-luteal (d 1 to 5), mid-luteal (d 6 to 10), late-luteal (11 to 15), periluteolytic (-1, 0, +1 d relative to progesterone decline), and follicular (5 d prior to fifth estrus) phases of the estrous cycle. The number of CL during the sampling estrous cycle was greater (P < 0.005) for the high vs low OR gilts (18.8 vs 14.3) and again (P < 0.001) in the cycle subsequent to hormone measurement (20.9 vs 14.7). For high-OR gilts, FSH was greater during the ovulatory period (P = 0.002), the mid- (P < 0.05) and late-luteal phases (P = 0.01), and tended to be elevated during the early-luteal (P = 0.06), but not the luteolytic or follicular periods. LH was greater in high-OR gilts during the ovulatory period (P < 0.005), but not at other periods during the cycle. In high-OR gilts, progesterone was greater in the mid, late, and ovulatory phases (P < 0.005), but not in the follicular, ovulatory, and early-luteal phases. Concentrations of estradiol-17beta were not different between OR groups during the cycle. Inhibin was greater for the high OR group (P < 0.005) during the early, mid, late, luteolytic, and follicular phases (P < 0.001). The duration of the follicular phase (from last baseline estrogen value to the LH peak) was 6.5 +/- 0.5 d and was not affected by OR group. These results indicate that elevated concentrations of both FSH and LH are associated with increased ovulation rate during the ovulatory phase, but that only elevated FSH during much of the luteal phase is associated with increased ovulation rate. Of the ovarian hormones, both inhibin and progesterone are highly related to greater ovulation rates. These findings could aid in understanding how ovulation rate is controlled in pigs.     

Ovarian function and hormone secretion of gilts actively immunized against androstenedione

Fifty crossbred gilts immunized against bovine serum albumin (BSA) or androstenedione conjugated to BSA (AD) were used in three experiments. Primary immunizations were given at 120 d of age and boosters at 148 and 176 d. Gilts were moved to pens containing four to five animals each and exposed to boars beginning at 180 d of age. Immunization against AD did not affect age at puberty, percentage of gilts exhibiting estrus or duration of first estrous cycle. Over the three experiments, ovulation rate was 24% greater for AD-immunized gilts than for controls, and the number of corpora lutea was related positively (r = .82) to the log of the antibody titer. Number of ovulations decreased as interval from booster immunization to onset of estrus increased. During diestrus of the first estrous cycle, gilts immunized against AD had more follicles 5 to 10 mm in diameter, more total ovarian follicles and more total ovarian structures (corpora lutea plus follicles) than controls. Immunization against AD increased the frequency of LH pulses on d 16 but not on d 17 or 18, of the estrous cycle. However, average serum concentrations of LH, FSH and estradiol from 5 d before until 2 d after expected estrus were not different between treatment groups. Concentrations of AD in follicles 4 to 6 and greater than 7 mm in diameter were greater in gilts immunized against AD. Mean serum progesterone was higher on d 9 and 12 after mating in AD immunized gilts than in controls. Immunization against AD had no effect on maintenance of pregnancy or embryo survival rate.     

Effects of charcoal-extracted, bovine follicular fluid on gonadotropin concentrations, the onset of estrus and luteal function in heifers

A study was conducted to determine the effect of charcoal-extracted, bovine follicular fluid (CFF) on plasma follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations, the interval from luteolysis to estrus, and subsequent luteal function in heifers. Fifteen Angus, Simmental and Hereford heifers were allotted by age, weight and breed to a control (C, n = 8) or a CFF (n = 7) group. Heifers received injections of saline or CFF (iv, 8 ml/injection) every 12 h from d 1 (d 0 estrus) through d 5 of the estrous cycle. On d 6, each heifer was injected (im) with 25 mg of prostaglandin F2 alpha (PGF2 alpha). Blood samples were collected every 12 h by venipuncture starting just before the first saline or CFF injection and continuing until estrus. Thereafter, blood samples were collected every other day during the subsequent estrous cycle and assayed for FSH, LH, estradiol-17 beta and progesterone by radioimmunoassay. Injections of CFF had no effect (P greater than .05) on circulating FSH or LH concentrations from d 1 to 5 relative to the C group; however, there was a transient rise (P less than .05) in FSH concentrations 24 h following cessation of CFF injections. This transient rise in FSH was not immediately followed by an increase in plasma estradiol-17 beta concentrations. Although CFF injections did not interfere with PGF2 alpha-induced luteolysis, the interval from PGF2 alpha injection to estrus was delayed (P less than .05) by 5 d in the CFF group compared with the C group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in plasma follicle-stimulating hormone, luteinizing hormone, estrogen and progesterone during growth of ovulatory follicles in the pig

This experiment was conducted to determine the changes in secretion of LH, FSH, estrogen and progesterone during follicle maturation. Ovaries were recovered from 11 non-treated (control) gilts, three on day 13, four on day 16, and four on day 19 of the estrous cycle, and from four altrenogest-treated gilts on day 19. Altrenogest, a progesterone agonist, was fed at a dose of 20 mg once daily from days 13 to 18 to block spontaneous follicle maturation. Gilts were bled daily from day 12 until slaughter. For control gilts, the number of follicles/gilt 1-6 mm in diameter decreased (P less than .05) from 93.5 on day 13 to 21.5 on day 19, and the number of large (greater than 6 mm) follicles increased (P less than .05) from 5.3 to 13.2. Altrenogest treatment blocked loss of small follicles and growth of large follicles between days 13 and 19. Plasma progesterone decreased (P less than .001) between days 12 and 16 in both control and altrenogest-treated gilts. Plasma FSH decreased (P less than .05) between days 12 and 16 only in control gilts. Plasma LH was not significantly affected by day or altrenogest treatment. Plasma estrogen increased (P less than .05) between days 15 and 19 only in control gilts. These results indicate that 1) no increased LH secretion was detected in conjunction with emergence of ovulatory follicles, and 2) atresia of nonovulatory follicles was associated with decreased secretion of FSH. Both atresia and decreasing FSH secretion began before estrogen concentration increased in the systemic circulation.     

Effect of dietary energy restriction on metabolic and endocrine responses during the estrous cycle of the suckled beef cow

A replicated trial was conducted with suckled Angus and Polled Hereford cows (110 d postcalving) to determine metabolic and endocrine responses to an energy-restricted diet after cows had re-established postpartum estrous cyclicity. Cows were individually fed 26.5 Mcal ME (H) or 15.2 Mcal ME (L) for a 30-d preliminary period and fitted with an indwelling jugular cannula at synchronized estrus. Average daily weight change during the estrous cycle was .60 +/- .25 and -1.37 +/- .30 kg/d for H and L, respectively (P less than .05). Blood concentrations of cortisol, progesterone and LH during the estrous cycle were not affected by diet, nor did diet affect frequency or amplitude of LH pulses (P greater than .05). No dietary differences were observed for daily concentrations of total protein, glucose, nonesterified fatty acids or acetate. Mean blood concentrations of propionate and butyrate were not different between diets; however, L cows had lower concentrations of propionate and butyrate on d 11 of the cycle (P less than .05). Cows fed L had higher concentrations of blood urea nitrogen (P less than .05), but they had lower concentrations of cholesterol (P less than .05) on d 4, 11, 18 and subsequent estrus (E). Insulin was not different on d 4 and 11; however, cows fed L had lower insulin concentrations on d 18 and d E (P less than .05). Dietary energy restriction in these cyclic cows caused no change in endocrine responses. Of metabolic responses measured, only blood urea nitrogen, cholesterol and insulin showed consistent changes.     

Follicular fluid concentrations of estradiol-17 beta and progesterone and secretory patterns of LH and FSH in prepubertal gilts reared in confinement or outdoor lots

One-hundred-twenty crossbred gilts from two experiments were assigned randomly to a 2 X 5 factorial experiment. Gilts were reared in two environments (confinement or outside) and assigned to be slaughtered at 4, 5, 6, 7 or 8 mo of age. Beginning at 6 mo of age, blood samples were taken at weekly intervals from each gilt via venipuncture. Serum concentrations of progesterone were analyzed to determine when gilts attained puberty. On the day prior to slaughter, six pigs within a treatment group were cannulated and blood samples were taken at 20-min intervals for 4 h. At slaughter, follicular fluid (FF) was aspirated and the volume determined from those follicles having a diameter of at least 4 mm. No effect of environment was found on the proportion of gilts that attained puberty by 8 mo of age. For the 12 gilts that reached puberty during the study, the age at puberty for gilts reared in outdoor lots (202 +/- 5 d) was less (P less than .05) than those reared in confinement (224 +/- 8 d). Mean concentrations of serum luteinizing hormone (LH; P = 98) and number of secretory spikes of LH (P = .76) were similar between gilts reared in confinement and those reared in outdoor lots. No differences in average serum concentrations of follicle stimulating hormone (FSH) or number of secretory spikes of FSH were found between gilts subjected to these environments (P = .95). Concentrations of estradiol-17 beta in FF were not affected by environment or age (P greater than .25).(ABSTRACT TRUNCATED AT 250 WORDS)     

Factors contributing to early embryonic mortality in gilts bred at first estrus

Gilts bred at first (n = 18) and third (n = 18) estrus were assigned in replicates of equal numbers to be slaughtered on d 3, 15 and 30 post-mating to assess fertilization rate, embryonic losses and serum concentrations of estrogen (estradiol-17 beta + estrone) and progesterone. Mean number of ovulations was lower among gilts bred at first vs third estrus (12.2 vs 14.5; P less than .05), with no difference in fertilization rate (100 vs 98%). Embryonic survival was lower (P less than .05) among gilts bred at first vs third estrus on d 15 (78.1 vs 95.4%) and 30 (66.7 vs 89.4%) of gestation. Serum estrogen (pg/ml) and progesterone (ng/ml) levels, although lower in gilts bred at first vs third estrus, were not significantly different at the three stages of gestation studied. The ratio of progesterone to estrogen in gilts bred at first estrus was higher than in those bred at third estrus on d 15 (439 +/- 71 vs 210 +/- 17) and 30 (597 +/- 106 vs 179 +/- 50), but was lower on d 3 (187 +/- 37 vs 444 +/- 123; stage of gestation X estrous period interaction, P less than .05). These data suggest that changes in the ratio of systemic levels of estrogen and progesterone may be related to early embryonic mortality in gilts bred at pubertal estrus.     

Effects of exogenous estradiol-17 beta on luteinizing hormone, progesterone, and estradiol-17 beta concentrations before and after prostaglandin F2 alpha-induced termination of pregnancy and pseudopregnancy in gilts.

This study evaluated the influence of exogenous estradiol-17 beta (E2) administration on LH concentrations and the number of animals returning to estrus after the termination of pregnancy or pseudopregnancy in gilts. Gilts were mated (pregnant; n = 11) on the 1st d of estrus or received 5 mg of estradiol valerate i.m. at d 11 to 15 after the onset of estrus (pseudopregnant; n = 9). Gilts were treated with prostaglandin F2 alpha (PGF2 alpha, 15 and 10 mg) at 12-h intervals on d 44 of pregnancy or pseudopregnancy. The day of abortion or luteolysis (progesterone less than .2 ng/mL) was considered d 0. Six pregnant and four pseudopregnant gilts received s.c. an E2 capsule (24 mg of E2) on d -20 and additional E2 capsules on d -13 and -6. The E2 capsules were removed on the day after PGF2 alpha administration. Blood samples were collected at 12-h intervals from d -21 to -3, at 6-h intervals from d -2 to 21 or the onset of estrus, and at 15-min intervals for 8 h on d -2, 1, 4, 7, 10, 14, and 18. After each 8-h sampling period, gilts were treated i.v. with GnRH at .5 micrograms/kg of BW and blood samples collected at 10-min intervals for 3 h. A greater (P less than .05) proportion of sham-treated gilts than of E2-treated gilts exhibited a preovulatory-like LH surge after abortion/luteolysis. It was evident that E2 supplementation before luteolysis reduced the ability of pregnant and pseudopregnant gilts to return to estrus.     

Reduction in age of puberty in gilts consuming melatonin during decreasing or increasing daylength

Two experiments were conducted to determine whether oral administration of melatonin alters the onset of puberty in gilts during naturally increasing or decreasing daylength. In Exp. 1, 20 crossbred prepubertal gilts weighing 77.5 +/- .5 kg at 171.8 +/- 1.0 d of age were assigned randomly to receive either a daily oral dose of 3 mg of melatonin (MEL) or ethanol vehicle (ETH) at 1530 from August 31 to December 1, 1987 (decreasing daylength). Gilts were exposed to mature boars for 20 min thrice weekly and blood samples were collected twice weekly. Serum concentrations of progesterone were used to establish age at puberty and length of estrous cycle. In Exp. 2, 20 crossbred prepubertal gilts weighing 67.7 +/- .7 kg at 143.8 +/- 1.1 d of age received either MEL or ETH treatment from February 1 to May 15, 1988 (increasing daylength). Age of puberty was less in gilts that received MEL than in gilts that received ETH in both Exp. 1 (198 +/- 3 vs 228 +/- 7 d; P less than .01) and Exp. 2 (183.8 +/- 2.7 d vs 194.3 +/- 3.3 d; P less than .05). Gilts that received MEL reached puberty at a lighter weight than gilts that received ETH in Exp. 1 (95.6 +/- 2.1 vs 112.4 +/- 3.9 kg; P less than .01) and Exp. 2 (88.1 +/- 1.5 vs 96.0 +/- 1.8 kg; P less than .01). Serum concentrations of LH and FSH, length of estrous cycles, and percentage of muscle of carcasses were similar between MEL and ETH gilts.(ABSTRACT TRUNCATED AT 250 WORDS)     

Follicle-stimulating hormone (FSH) during the secondary surge in gilts as influenced by administration of porcine follicular fluid (pFF)

The effect of volume and frequency of administration of porcine follicular fluid (pFF) on FSH concentration was determined in mature gilts during the period of the secondary FSH surge (d 0 to 5; d 0 = onset of estrus) and following withdrawal of pFF (d 5.5 to 9). Crossbred gilts (n = 14) were randomized in a 3 x 2 factorial treatment design involving three doses of pFF (0, 5, or 10 ml) and once- vs twice-daily pFF administration. Porcine FF was aspirated from medium and large follicles and treated with 5 mg of activated charcoal per milliliter of pFF to remove steroids. Once-daily administration of pFF, regardless of dose, failed to suppress mean concentrations of FSH during the secondary FSH surge. Treatment of gilts twice daily with 10 ml of pFF suppressed (P less than .05) area under the FSH curve during the secondary FSH surge compared with gilts given saline. Gilts treated twice daily with 5 ml pFF showed comparable suppression of plasma FSH from d 0 to 3 but began to overcome FSH inhibition after d 3. As a result, FSH release only tended to be lower than controls for the entire treatment period (P less than .1). Mean FSH concentrations were increased (P less than .05) during the post-treatment period (d 5.5 to 9) by treatment with intermediate (5 ml pFF, two times daily and 10 ml pFF, one time daily) and high (10 ml pFF, two times daily) doses of pFF. Neither ovulation rate nor interestrous interval was affected by pFF administration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lack of an association between plasma follicle-stimulating hormone concentrations and ovarian weight in prepubertal gilts

Selection for increased number of corpora lutea in gilts is associated with increased plasma FSH concentrations during pubertal development. In the current study, 270 gilts from a control (CO) line and a line selected for increased ovulation rate (OR) were unilaterally ovariectomized at 85 d of age, and this ovarian weight was related to FSH concentrations at 65, 75, and 85 d of age. Gilts were produced during two farrowing seasons, spring and fall, and the age at first estrus was monitored from 160 to 250 d. Plasma FSH was greater in OR than in CO gilts at 65 (P < 0.01) and 75 d (difference in spring greater than in fall, P < 0.01), but FSH at these ages was not correlated with ovarian weight at 85 d. At 85 d, FSH did not differ in gilts of these lines; however, FSH was negatively correlated (r = -0.27, P < 0.01) with ovarian weight. The proportion of gilts detected in estrus was less for spring-born CO gilts than for spring-born OR or for fall-born CO and OR gilts (78 vs. 92%, season x line, P < 0.02). The age at first estrus was similar in the two lines but was earlier (P < 0.01) for spring-born than for fall-born gilts (194 vs. 204 d). Concentrations of FSH at each of the ages examined were not correlated with the age at first estrus. These observations support the conclusion that selection for a greater number of corpora lutea produces a correlated increase in plasma FSH during early pubertal development. This increase in FSH most likely reflects differences in FSH synthesis and release and not differences in the stage of pubertal development.     

Ovulation and embryonic survival in pubertal gilts treated with gonadotropin releasing hormone

An experiment was conducted to evaluate the effect of exogenous gonadotropin releasing hormone (GnRH) on ovulation and embryonic survival in pubertal gilts. Gilts were assigned in replicates to a control (n = 10) and treatment (n = 10) group. Treatment consisted of an iv injection of 200 micrograms of GnRH immediately after initial mating on the first day of detected estrus. Control gilts were similarly injected with physiological saline. Blood samples were collected from the anterior vena cava immediately prior to injection, thereafter at 15-min intervals for 90 min, and subsequently, before slaughter on d 30 of gestation. Serum samples were analyzed for luteinizing hormone (LH) and progesterone by radioimmunoassay. Treatment with GnRH increased the quantity of LH released (P less than .05), with highest serum concentrations (ng/ml, means +/- SE) of gonadotropin in treated gilts (17.3 +/- 3.5) occurring at 75 min post-injection. In control gilts, serum concentrations of LH were not affected by injection of saline. Mean number of ovulations in treated gilts was also greater (P less than .05) than that of control animals (14.5 +/- .7 vs 12.1 +/- .6). However, treatment with GnRH did not enhance the number of attached conceptuses (normal and degenerating) present (treated, 10.9 +/- .9 vs control, 10.5 +/- .7) nor the percentage of viable fetuses (treated, 74.7 +/- 6.9 vs control, 83.5 +/- 5.0%) on d 30 of gestation. Although GnRH increased ovulation rate, mean weight of corpora lutea of treated and control gilts did not differ (402.8 +/- 16.3 vs 389.5 +/- 11.3 mg, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of prepubertal consumption of zearalenone on puberty and subsequent reproduction of gilts

Forty-eight prepubertal gilts (178.7 +/- 4.1 d; 94.2 +/- 4.1 kg), 16 in each of three trials, were assigned randomly to receive 0 (C) or 10 ppm zearalenone (Z) daily in 2.5 kg of a 14% protein finishing ration for 2 wk. Blood samples were collected at 20-min intervals for 4 h 1 wk after the start of the experiment and 1 wk after Z was withdrawn. Two weeks after Z was withdrawn, gilts were exposed to mature boars 15 min per day for 3 wk. Gilts in estrus were mated to two different boars 12 h apart. Twice each week, blood was sampled and analyzed for progesterone to establish age of puberty. Age at puberty differed (P = .008) among replicates but was similar (P = .13) between Z and C gilts within each replicate. Mean serum concentrations of LH were suppressed (P = .025) during consumption of Z (.25 vs .42 ng/ml) but were similar (P = .16) to concentrations in C gilts 1 wk after Z was withdrawn (.35 vs .45 ng/ml). Frequency and amplitude of LH secretory spikes did not differ (P greater than .50) between Z and C gilts during either sampling period. Mean serum concentrations of FSH were similar (P = .25) between Z and C gilts. Number of corpora lutea and live fetuses were similar (P = .29 and P = .94, respectively) between Z and C gilts. Fetal weights were greater (P = .025) and crown to rump length tended to be greater (P = .10) in fetuses from Z gilts.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of constant versus adjusted dose of exogenous porcine growth hormone (pGH) on growth and reproductive characteristics of gilts

Growth, carcass traits, and selected reproductive characteristics were evaluated in prepubertal gilts treated with either a constant mass of pGH or a mass of pGH adjusted periodically for changes in BW. Gilts (64 kg, n = 24) were given 24 daily injections of either vehicle (C; control) or one of two doses of pGH: 70 micrograms/kg of BW, with dose adjusted every 5th d for changes in BW (A; adjusted), or 70 micrograms/kg of initial BW (U; unadjusted). Gilts were slaughtered on d 25. Gilts treated with pGH had higher ADG (P less than .002) and improved feed efficiency (kg of feed/kg of gain; P = .0003) compared with controls. Weights of adrenal glands, liver, heart, and kidney were higher (all P less than .01) for Groups A and U than for Group C gilts. Average backfat thickness was less (P less than .004) for A and U gilts than for C gilts and less for Group A than for Group U (P less than .02). Furthermore, growth and carcass traits were similar (P greater than .05) for Groups A and U, except for measurements of first rib backfat, last rib backfat, and average backfat depth (P less than .05). Culture of granulosa cells (GC) was employed to assess ovarian function. Addition of FSH to the culture media enhanced secretion of progesterone (P4) by cultured GC from all in vivo treatments compared with unsupplemented cultures of GC (P less than .05). Addition of LH to the culture media enhanced secretion of P4 by cultured GC from pGH-treated gilts only (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of daily injections of porcine somatotropin on growth, puberty, and reproduction in gilts

To determine whether recombinant porcine somatotropin (rpST) alters reproduction, 40 crossbred gilts weighing 59.1 +/- .5 kg at 125 +/- 1 d of age were assigned randomly to an experiment arranged as a 2 x 2 factorial. Eight gilts were given daily injections of diluent until they reached 104 kg BW (DW), and eight received diluent injections until puberty (DP). Twelve gilts were given rpST (4 mg/d) until 104 kg BW (PW) and 12 were given rpST injections until puberty (PP). All gilts were individually fed on an ad libitum basis an 18% CP corn-soybean meal diet (1.2% lysine and 3.1 Mcal/kg of ME). Beginning at 5 mo of age, gilts were exposed 20 min daily to mature boars. Serum concentrations of progesterone were measured weekly from 5 to 8 mo of age to verify age of puberty. Gilts observed in pubertal estrus were mated to two different boars 10 h apart. At 47 +/- 1 d of gestation, gilts were slaughtered to assess fetal development. After 60 d of treatment, serum LH and FSH profiles were determined in blood samples drawn at 20-min intervals for 4 h from eight diluent- and eight rpST-treated gilts fitted with indwelling jugular catheters. By 28 d, feed intake, feed/gain, and blood urea nitrogen were decreased (P less than .005) by rpST. Treatments did not affect (P greater than .05) the proportion of gilts attaining first ovulation (DW = 6/6; DP = 10/10; PW = 7/9; PP = 14/14) or conception rate (DW = 5/6; DP = 7/10; PW = 4/6; PP = 11/12).(ABSTRACT TRUNCATED AT 250 WORDS)     

The influence of ovariectomy on luteinizing hormone concentrations in anestrous and cyclic sows

In an effort to determine whether anestrus in swine is due to aberrant ovarian feedback control of gonadotropin release, this study contrasted the influence of ovariectomy on LH concentrations in serum of anestrous sows and in sows that returned to estrus following weaning. Blood samples were collected at 6-h intervals from 7 d prior to until 4 d after ovariectomy of 22 anestrous and 24 cyclic sows. Blood samples also were collected at 15-min intervals for 8 h at 2 d prior to and 2 d after ovariectomy. Sampling at 6-h intervals continued until 12 d after ovariectomy and additional 8-h windows of 15-min samples were taken at 7 and 12 d after ovariectomy of seven anestrous and nine diestrous sows. Mean LH concentrations and LH pulse frequencies were greater (P less than .05) 2 d after ovariectomy than 2 d prior to ovariectomy in both anestrous and diestrous sows. Mean pulse amplitude had increased by 2 d after ovariectomy in anestrous sows but did not change in cyclic sows. Baselines as determined from the mean of all LH measurements excluding pulses, remained the same in both anestrous and diestrous sows at 2 d after ovariectomy. Pulse frequency, pulse amplitude, and mean LH concentration were greater (P less than .05) in both anestrous and diestrous sows at 7 and 12 d after ovariectomy than at 2 d prior to and 2 d after ovariectomy. Pulse amplitude on d 7 and 12 after ovariectomy decreased (P less than .05) in both anestrous and diestrous sows relative to those observed at earlier times.(ABSTRACT TRUNCATED AT 250 WORDS)